A Diablo 4 player is already showing the way for others to optimise their Nightmare Dungeon grind for loot and experience gains following a recent patch, and for that, I'm truly thankful.
Diablo 4 patch 1.0.3 delivers on a promise by Blizzard to make Nightmare Dungeons a more appealing way to grind experience points in the late game. Completing a Nightmare Dungeon now rewards "slightly increased" experience gains for slaying monsters and dungeon completion. Better yet, you can teleport to any Nightmare Dungeon straight from the map.
While that's all good stuff, it changes which dungeons are more worth your time than others. A huge part of loot-driven games like Diablo and Destiny for goblins like myself is optimising the grind. For example, a nightmare dungeon that took ages to get to was previously no good in Diablo 4. That few minutes of travel time? That's wasted farming time, bud.
One Diablo 4 player, though, has already devised an elaborate method to sort the wheat from the chaff. Zehnpae explains on Reddit that they're scoring each dungeon's front half, back half, boss or event offering, and general enemy density. So, if a Nightmare Dungeon doesn't have a boss or event in its middle section, it's probably scoring high in that category. If general enemies are well-grouped and squishy, it's scoring high there too.
Considering each tier is scored out of four, the best dungeons you can do for optimised grinding are Ancient's Lament, Blind Burrows, Champion's Demise, Earthen Wound, Renegade's Retreat, and Sunken Ruins.
Happy grinding.